1. Field of the Invention
The invention relates to a method and apparatus for performing laser surgical procedures.
2. Description of Related Art
Contemporary medical practice involves the use of two types of lasers in surgery. One type of laser cuts tissue by applying an intense amount of heat to a small area. Over the past decade three different lasers have emerged as significant for this type of application. They are the argon ion laser that emits in the blue-green portion of the spectrum 0.45 to 0.53 microns, the Nd:YAG laser with its primary emission level at 1.06 and 1.32 microns in the near infrared portion of the spectrum and the CO.sub.2 laser that emits at a wavelength of 10.6 microns, well into the infrared portion of the spectrum. Of these three lasers, the CO.sub.2 laser has a number of advantages. For example, it is over an order of magnitude more efficient than either the Nd:YAG or the argon ion laser and it has been found to be best suited for cutting tissue.
However, application of the CO.sub.2 laser has been hampered by lack of a commercially viable flexible beam delivery means similar to the silica optical fibers that work so well with the Nd:YAG and argon ion lasers. Silica optical fibers are simply not transparent at the 10.6 micron emission wavelength of the CO.sub.2 laser. Major efforts in laboratories around the world have been expended to perfect optical fibers of materials that would be suitable for guiding the 10.6 micron beam. Unfortunately, all efforts to date have been frustrated by lack of sufficient transparency, lack of sufficient flexibility, excessive toxicity and/or insufficient lifetime. Other efforts have been placed on making hollow metal or metal clad dielectric waveguides. These guides are very transparent when straight, but their losses increase substantially when the guides are bent to even a modest radius of curvature.
In frustration over the lack of suitable delivery systems for the CO.sub.2 laser in surgical applications, it has been proposed to use CO lasers which emit at 5.3 microns rather than 10.6 microns. The shorter wavelength of the CO lasers increases the number of candidate materials that might be selected for optical fiber delivery systems. Although there are more possibilities, there still is no material for transmission at 5.3 microns which gives comparable performance to conventional silica optical fibers at one micron. In addition, at its present state of development, the CO laser is substantially less reliable than current CO.sub.2 lasers.
A second type of laser for surgical applications emits ultraviolet radiation at ultraviolet wavelengths which break the chemical bonds of the tissue and converts the tissue directly into gas with very little heating. The lack of heat makes these lasers particularly useful in microsurgical procedures. An example of this type of laser is the excimer laser which typically emits radiant energy at wavelengths in the range of 0.15 to 0.36 microns. Particularly strong emissions can be achieved at 0.193 and 0.248 microns. One of the last hurdles for the excimer laser is finding a suitable flexible delivery medium. Optical absorption in conventional silica optical fibers is too high for procedures that require fibers more than about one foot long. However, to perform a wide variety of surgical procedures requires fibers that are about two meters long.
Before lasers were used for surgical applications, there were a number of different types of endoscopes that were designed so that a surgeon could see inside the human body through a small opening. This was a great aid in diagnosis. The first of these viewing endoscopes was made in a semirigid, tubular structure for straight or almost straight line of sight. These scopes were usually made with an outer thin wall stainless steel tube that contained a number of lenses. Flexibility of these scopes was limited by buckling of the stainless steel tube. As time went on, the need for a more flexible viewing endoscope was recognized. However, rather than extend the semirigid scope technology, the medical field was quick to adopt bundles of silica fibers as the means for obtaining flexible viewing. The bundles have the individual fibers located at the same relative positions at both ends, so that images can be propagated without lenses. This type of assembly, with carefully positioned fibers, is known as a coherent bundle. These bundles worked so well for flexible viewing that there was no motivation for further development of the semirigid endoscope technology to obtain more flexible structures. Unfortunately, as previously described, silica fibers are not satisfactory for transmitting surgical laser beams.
It is, therefore, apparent that there is a need in the art for a flexible delivery medium which is capable of delivering emissions from the two types of lasers used in surgical applications, particularly the infrared emissions from a CO.sub.2 laser and ultraviolet emissions from an excimer laser.